Swift Timer App - ios

Question

I was trying to build a simple ios timer app using swift3. I successfully created an app using the following code. It has three buttons, one to start the timer, one to stop the timer which means reset and one to pause the timer. all the buttons are working but when I click on start once again while the timer is running, the timer interval speeds up (means calls the selector function twice within a second). how to solve this problem.
Here is my code
#IBOutlet weak var lbl: UILabel!
var time = 0
var timer = Timer()
#IBOutlet weak var start: UIButton!
#IBOutlet weak var stop: UIButton!
#IBOutlet weak var pause: UIButton!
#IBAction func start(_ sender: AnyObject) {
timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(ViewController.action), userInfo: nil, repeats: true)
}
#IBAction func stop(_ sender: AnyObject) {
//timer.invalidate()
time = 0
lbl.text = "0"
}
#IBAction func pause(_ sender: AnyObject) {
timer.invalidate()
}
override func viewDidLoad() {
super.viewDidLoad()
}
func action() {
time += 1
lbl.text = String(time)
}

Answer 1

If your start method runs while a timer is already active, you create a second timer. Now you have two timers calling the same action, which accounts for your problem. Scheduled timers are retained by their run loops, so even though you don't have a reference to the old timer, it's still there.
At a minimum you need to either invalidate the old timer or else just keep using the one you have. But there are some things that would help make the code better:
Your timer attribute should probably be a Swift optional. Initializing it as Timer() doesn't do anything useful. It would make more sense if timer could be nil when no timer should be running.
You should probably disable your "start" button when a timer is running. It doesn't make sense for it to be active when the timer has already started. You could do this by setting up an IBOutlet for the button and changing the value if the button's isEnabled property.

Answer 2

One Mistake in Source code.
First Stop exist timer then start new timer.
Code for that is below.
#IBAction func start(_ sender: AnyObject) {
timer.invalidate()
timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(ViewController.action), userInfo: nil, repeats: true)
}
And for stop timer use invalidate timer function.
#IBAction func stop(_ sender: AnyObject) {
timer.invalidate()
}

Answer 3

I think what you need to do is invalidate if there is a timer running
#IBAction func start(_ sender: AnyObject) {
if (timer) {
timer.invalidate()
}
timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(ViewController.action), userInfo: nil, repeats: true)
}

Answer 4

#IBOutlet weak var lbl: UILabel!
var time = 0
var timer : Timer?
var isPause = false
#IBOutlet weak var start: UIButton!
#IBOutlet weak var stop: UIButton!
#IBOutlet weak var pause: UIButton!
#IBAction func start(_ sender: AnyObject) {
timer?.invalidate()
timer = nil
isPause = false
time = 0
lbl.text = "0"
// or call stop(self.stop)
timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(ViewController.action), userInfo: nil, repeats: true)
}
#IBAction func stop(_ sender: AnyObject) {
timer?.invalidate()
timer = nil
isPause = false
time = 0
lbl.text = "0"
}
#IBAction func pause(_ sender: AnyObject) {
timer.invalidate()
isPause = !isPause // second click to resum...
}
override func viewDidLoad() {
super.viewDidLoad()
}
func action() {
if !isPause {
time += 1
lbl.text = String(time)
}
}